Parasitic mites have caused serious problems both for the beekeeping industry and more broadly in agriculture, since honeybees are important for pollination of many important crops. There are two types of parasitic mites that cause problems for honeybees. Both Varroa jacobsoni and the tracheal mite Acarapis woodi cause infestations that have resulted in extensive reductions in honeybee populations. The successful management of honeybees in the face of these pests requires multiple approaches for control, including breeding of resistant strains and various treatments and control measures.
Various treatments have been attempted to control parasitic mites in honeybees, although limitations of currently available treatments include toxicity of the chemicals used, marginal effectiveness, inconvenience of use, difficulties in registration of the composition with environmental agencies, mite resistance, and/or contamination of beeswax. There are currently two products registered in the United States for control of Varroa: Apistan®. (Wellmark International, Dallas, Tex.), a plastic strip containing fluvalinate, and CheckMite+™ (Bayer), a plastic strip containing coumaphos. In addition, another product, called Api Life Var, containing thymol, is available in a few states. This product is stated to be only 75% effective, so does not provide a complete treatment. Unfortunately, there are now strains of mites that are resistant to both fluvalinate and coumaphos. Furthermore, there are concerns about contamination of honey and beeswax with these agents.
Other treatments have been used on an experimental basis with varying results. Essential oils have been used with mixed success. Experimental work has been carried out with an ester of formic acid, methylformate. Results of that work are unknown at the present time. Tracheal mites can sometimes be controlled with menthol or, less effectively, by use of vegetable oil patties placed in the hive. However, none of these materials is active against both types of parasitic mites.
Formic acid has been used quite effectively in much of the world to control mite infestation, but it is not currently registered for use in the United States. Formic acid vapors are known to be effective for controlling parasitic mites in honeybees. However, formic acid is corrosive and toxic; thus, using it can be hazardous for the user. Methods and compositions for application of formic acid have taken a variety of forms, including liquid, support materials soaked in liquid formic acid, strips of formic acid, and menthol-paste.
Formic acid has been used in liquid form in Europe and Canada and has been shown to control parasitic mites of honeybees in a wide variety of situations. The first comprehensive report on such use of formic acid appeared in a special issue on varroatosis (Ritter and Ruttner. 1980. Allg. Dtsch. Imkerztg. vol. 14, pp. 151–153). Subsequently, the “Illertisser Mite plate” (IMP), a cardboard-like material that could be soaked with formic acid and placed in the hive was developed (Wachendorfer et al. 1985. Apidologie. vol. 16, pp. 291–306). This method, or modifications of it, was tested against parasitic bee mites in a number of countries, including Germany (Hoppe et al. 1989. Amer. Bee J. vol 129, pp. 739–742), Sweden (Fries, I. 1989. Swedish J. Agric. Res. vol. 19, pp. 213–216) and Dubai (Bracey and Fisher. 1989. Amer. Bee J. vol. 129, pp. 735–737). Other known application methods have included soaked cheesecloth (Liu and Nasr. 1992. Amer. Bee J. vol. 132, pp. 666–668) and containers with wicks (Sharma et al. 1983. Indian Bee J. vol. 45, pp. 1–2; Lupo and Gerling. 1990. Apidologie. vol. 21, pp. 261–267). Nelson et al. (1994. Bee Science. vol. 3, no. 3, pp. 128–134) disclosed formic acid application for controlling tracheal mites and compared treatments using liquid formic acid, formic acid gel-strips, menthol-paste and the German product IMP.
Most of the above-mentioned methods use varying concentrations of dilute liquid formic acid, and most require multiple applications. In addition, use of the IMP apparatus often necessitates the removal of part of the honeycomb from the hive to meet space requirements.
Another approach that has been developed for dispensing formic acid involves mixing either polyacrylic acid or fumed silica with a formic acid solution to make a gel. This approach is described in U.S. Pat. No. 6,037,374 and in J Agric Food Chem 47(9): 3850–3 (1999). This technology was also developed into a commercial product that was registered for use in the United States under the trade name Apicure™ (BetterBee). However, due to problems of leakage from the packaging, it was removed from the market after a short time.
There have been numerous reports indicating the effectiveness of formic acid in gel for controlling parasitic mites in honeybees (Vet Parasitol 111(2–3):241–5 (2003) and J Vet Med B 48(1):11–4 (2001). Formic acid is very corrosive and safely dispensing it inside the beehive has been problematic. Moreover, because formic acid is a strong acid, it can destroy gelling agents and/or prevent adequate gel stability (thus resulting in failure to form a stable gel, leakiness of the resulting gel, and other similar stability problems). Formic acid can be difficult to mix with other reagents as well, which can also contribute to instability problems of resulting gels. Further, current methods can require handling liquid formic acid, frequent applications and/or extensive hive manipulation.
In addition to the above concerns, there is increasing resistance by Varroa to the currently approved products. If additional effective treatments were available, this could provide the ability to alternate treatment courses, thus minimizing the occurrence of such resistance.